1. Field of the Invention
This invention relates generally to fertilizers and to bioremediation and more specifically to the use of nutrients and micro-organisms for bioremediation.
2. Description of the Background
A goal of fertilizer manufacture is to produce chemically homogeneous granules that resist dusting and that are hard enough to resist crushing forces of at least pounds force. Hardness is a particularly useful quality of fertilizer granules used in agriculture and hardness (resistance to force) of greater than 4 pounds is particularly desired.
Historically, particulate fertilizers possessed a number of known defects, the most notable being the too rapid release of soluble plant food, causing phytotoxicity and the rapid depletion of the plant nutrients by leaching. Other problems included tendencies to cake and form dust. These problems are, for example reviewed in U.S. Pat. Nos. 3,475,154, 3,259,482, 3,264,088, 3,264,089, 4,711,659, and 4,772,490, and Japanese Patent No. 52-38361.
Most fertilizers, such as those that consist of or comprise ammonium sulfate, urea, diammonium phosphate or calcium phosphate are not manufactured specifically to have concentric layers. Some fertilizer granules are however made with specific coatings. These coatings help control the rate of nutrient release to treated soil and help prevent dusting of the granule itself. For example, U.S. Pat. No. 6,165,550 relates to the production of symmetrical fertilizer granules that are coated with polyurea-urethane to slow leaching of the granule nutrients into the soil. Other granules, as found in U.S. Pat. Nos. 5,679,129; 6,176,891 and 5,993,505, relate to a synthetic resin or polymer film on the surface of the granule to control the release of plant nutrients from the interior of the granule. Similarly, U.S. Pat. No. 6,187,074 relates to a coating of carboxyl-carrying ethylene copolymer to contain inorganic or organic fertilizer such that it is released slowly over time to the target crops.
Although biosolids have been processed into fertilizer, the methods used often require expensive processing to inactivate harmful or noxious substances. Some of these substances may arise during storage, and some form through air contact. Although not generally useful because of their cost, these fertilizers would be desirable because of the nutritional elements often present in the biosolids. Large scale use generally is prohibitive however, because of the cost.
Biosolids produced from municipal wastewater treatment usually are dried into irregular soil like preparations or alternatively dried into pellet forms. U.S. Pat. No. 5,849,060 relates to a dilute sulfuric acid or phosphoric acid to bind inorganic nutrients to a nucleus of water soluble fertilizer. As asserted in this patent, the outer coat of inorganics controls the release rate of the nutrient compounds by regulating the solubilities of the limited-soluble outer compounds. U.S. Pat. No. 5,766,302, describes granules that use an adhesive to stick an outer coating onto the surface of the underlying granule. U.S. Pat. No. 5,733,355, relates to the drying of bacteria and application of such to condition soil for plant cultivation, but does not specify a means of delivering said bacteria other than indicating a suitable carrier such as zeolite, diatomaceous earth or greenstuff. Greer et al. (U.S. Pat. Nos. 5,984,992 and 6,159,263) relates to rolling a melt of acid, water and sewage sludge into a granule which is then dried. U.S. Pat. No. 6,159,263 also relates to methods whereby zinc containing spent acids is used in the granule forming process to introduce zinc as a micronutrient into the granule. U.S. Pat. No. 6,331,300 relates to the use of porous particles impregnated with various nutrients or microorganisms for the facilitation of bioremediation. These patents address variations in pore size and length to control the rate of release of one type of impregnated substance. As there is only one type of substance per particle, multiple applications with several different types of particles generally is required to optimize effectiveness of bioremediation.